Impacts of climate change on the cryosphere, hydrological regimes and glacial lakes of the Hindu Kush Himalayas: a review of current knowledge

The climate and cryosphere of the Hindu Kush Himalayan (HKH) region have changed in the past and are very likely to change in the future. Warming of the climate system is unequivocal. The atmospheric concentration of greenhouse gases and short-lived climate pollutants has increased, the atmosphere and oceans have warmed, snow and ice have diminished, and the sea level has risen. The Himalayan region has the third largest amount of ice and snow in the world, after the Antarctic and Arctic, but these reserves are considered to be exceptionally vulnerable due to climate change. There is good agreement among global climate models (GCM) on future temperature trends in the region, but projections of future precipitation patterns differ widely. As a result, the demand for increased knowledge about likely future climate change is still high. Growing scientific knowledge and recent weather events show that extremes related to hydrological change can be substantial, although the geographical and temporal
resolution of the projected changes is still low in many areas.

This review provides a comprehensive overview of the present state of knowledge on climate change impacts on the cryosphere, hydrological regime, and glacial lakes of the Hindu Kush Himalayas at regional and basin scales, with a focus on the implications for hydropower development. It provides an insight into the limits in present understanding of the relevant natural processes, as well as the shortcomings in models, in situ measurements, and technologies in general.

It is clear that there is a considerable need for further research. The research questions vary from the general (e.g., how to improve broad scale climate modelling for the region) to the specific (e.g., future sedimentation and its role in hydropower plant longevity). The marked large spatial variation in the findings indicates the need to follow up at smaller scales. The research needs also vary in degree of importance of their role in improving effectiveness in hydropower development.

Many reports have discussed the potential for hydropower to transform the economies of the Himalayan region. But in order to develop this potential, it is essential to have good information on the likely scenarios for water availability and water related risks over many decades. A coordinated research programme is needed for the region that focuses more strongly on understanding the impacts of climate change at catchment and sub-basin levels, and specifically in those catchments/sub-basins which are candidates for hydropower development. ICIMOD and its partners should consider ways in which such a programme can be developed to cover the spectrum of research requirements that have become apparent in this review.